A conventional method consists in processing a sheet or plate of photosensitive glass by etching to form fine features on the head of an ink jet printer, for example. In particular, this method involves exposing desired portions of the photosensitive glass with ultraviolet radiation emitted by an ultraviolet lamp, heating the glass to 500.degree.-700.degree. C. to crystallize the exposed portions, and etching away the crystallized exposed portions with an etchant such as solution of hydrofluoric acid. A high-pressure mercury lamp is used as the ultraviolet lamp.
The conventional method is now described in further detail by referring to FIG. 10, where the ultraviolet lamp such as a high-pressure mercury lamp is indicated by 100. A plate of photosensitive glass 101 has a thickness less than 10 mm. The glass 101 is exposed with the ultraviolet radiation 100a emitted from the lamp 100 via a mask 102. The radiation penetrates through the glass plate from its front surface 101a to its rear surface 101b. When the glass plate is thermally developed, crystallized portions 103 extending from the front surface 101a to the rear surface 101b are formed. Therefore, during etching, the crystallized portions 103 are dissolved away by the etchant from the incident surface and from the opposite surface. This makes it impossible to write different shapes into opposite surfaces of the photosensitive glass plate 101.
In recent years, ink jet printer heads and other microelectronic devices have required microelectronic processing techniques. Such a head is fabricated from a thin plate or a sheet. It has been required that different fine features be written into opposite surfaces of the thin plate.
Accordingly, a new method has been developed. Specifically, tape is stuck to the rear surface 101b of the photosensitive glass plate 101 to prevent the etchant from touching the rear surface 101b. The front surface 101a is exposed to the etchant to form grooves. The etching depth is controlled according to the etching conditions such as the etching time, the temperature and the concentration of the etchant. However, the etch rate for the crystallized exposed portions is affected not only by the etching conditions but also by other factors such as the intensity of the exposing light and the thermal development conditions. Furthermore, the etch rate is affected by other various factors such as fatigue of the etchant, introduction of the dissolved photosensitive glass into the etchant during etching, and the manner in which the etchant touches the glass. Hence, it has been very difficult to control the etching depth.
Another problem is that the etched surfaces of the crystallized exposed portions a large surface roughness. In an ink passage formed in a surface of an ink jet printer head having large surface roughness, air bubbles introduced in the ink stagnate, thus adversely affecting the ink ejection characteristics.
Where photosensitive glass is etched in micromachining applications, large friction is produced. As a result, the mechanical driver portion cannot easily move.
In addition, it has been difficult to accomplish different etching depths in one etching process.